Q: How much is this device going to save me a day, month or year? How long will it take to pay for itself?

A: The daily solar power you put into the tank is basically taken off your power bill. So it depends on the wattage of your panels, solar conditions in your area and your hot water usage. Typical daily power requirements of a 40 gallon tank are almost 2 KWh just to keep it at temperature with no use. If you start using hot water it goes up from there! The savings add up daily and at the end of the month or year. You own the solar panels, they are worth something, you don't get that when you throw money at the power company.

Like a lot of other things, solar is an investment. You pay for it now and start to enjoy the benefits immediately and for years to come.

What else can you invest in that will keep on giving you a return for 25 to 35 years+ and you ALSO get to recoup your initial investment? Solar panels don't quit after their warranty expires, they lose only a little power over time.

And really, why does it have to pay for itself? Your car, fridge, air conditioner, lawn mower doesn't but you enjoy the benefits of those items.

At what point do you get any "payback" from the power company? Does anyone think about that?

Any power reducing modification on a piece of real estate will increase the property value.

Q: Why is it called a hybrid hot water heater?

A: You make your existing hot water heater a hybrid that uses both solar and grid electricity to help save on your power bill. Solar heats the water ALL DAY LONG and it adds up. Grid power would only be used to provide the power on dark days or to bring the heater up to temperature after a large use or for quick heat at night making it a "hybrid" or dual energy configuration. Modifications are easily reversible.

Q: Can you make a hot water heater combination with gas and electric to help save on the gas bill?

A: Yes! On a gas water heater you could set up a pre-heat tank, which is simply a small electric water heater connected in front of your existing gas water heater and running completely on solar. (in this case some plumbing is required)

Q: What about summertime when it's easier to heat the water?

A: Your system would perform better in the summer and depending on your solar panel wattage and personal usage, you could turn off the grid power and go with complete solar. For a pre-heat tank you could set up a bypass valve on your gas heater and turn off the gas for the season. You always want to have a blanket or two around the heater.

Q: How long does it take with about 750 Watts of solar panels to make my water hot for taking a shower or washing dishes?

A: At 750W with good sun it would take a few hours depending on the starting temperature, which may also depend on when the backup upper grid element came on last. The normal 4500W element generally runs for 10 to 15 minutes to "recover" using the grid, with solar it's longer but can come out to be the same over time. Running 750W for a hour is like running your 4500W element for 10 minutes on the grid. Solar adds up all day long, example, 750W all of hour 1 + 750W all of hour 2, etc.. So the upper grid backup heating element comes on less. 750W X 9 hours sun = 6,750 Wh or about 6.7 KWh a day off your bill, not bad, that's over 200 KWh a month! Time your use and conserve and you are in pretty good shape for what you spent on this low cost system. (your daily solar output may vary of course) If you go too high the thermostat may click off more and then you are wasting your investment in solar.

Q: How hard is it to install the Solar Hybrid Hot Water Controller?

A: It's basically 2 wires in (+/-) from the solar panels and 2 wires out to the heater. You should have basic electrical skills for DIY or contact an electrician, knowing how to hook up wires to things like home electric sockets and appliances and how to use a volt/ohm meter. For solar panel sets with a open voltage above 90V (75V is typical open voltage for "48V" panels), you would want to have an electrician wire it or strong house wiring electrical experience, know how to keep yourself insulated and have a solar disconnect switch outside at the solar panels. It's always good to have a helper nearby whenever you work on higher voltage home electrical devices. Hardware stores and YouTube have online videos showing how to do home electrical wiring.

Q: What solar panel size do you recommend and how many?

A: The typical minimum install would be two 24V 220W solar panels configured as "48V" (series circuit) = 440W. This could also be four 12V panels. Total panel wattage should be at least 250W or above for a typical 40 gallon tank. You need to consider that you are pumping power into the tank all day long and that can add up to the equivalent of a short run at full grid power (your daily solar output may vary of course). Around 440W is a good economical tradeoff between grid power, solar costs, and roof space used. If you go too high the thermostat may click off more and then you are wasting your investment in solar. With the minimal system you don't quite get the full power from your panels, this is part of the system cost tradeoff.

Most customers report that 750W is great for them, we recommend 750W if you have the space for the panels (and you should use the bigger box). You want the operating voltage at 60V or above for the standard 4500W element. Watch out for Mono Crystalline panels that have low VMPP (operating under load), Poly Crystalline is better and takes up less space. Always check the specs on the panel sticker, also see the Solar Hybrid Specs

Q: What wattage element should I have? Why is 4500W 240V recommended?

4500W 240V is common in most USA water heaters. It happens to be perfect for 750W of solar power, it's also pretty good at lower powers. It's a voltage and math thing.

If you get the voltage high enough other lower wattage elements start to become viable. Generally a 3800W 240V element would only give you about 625W out of your 750W (97.5V) of panels, but with 1000W (130V) of panels it will give you everything they can put out. As you go lower in element wattage the resistance increases and so does the need for higher voltages (generally for this situation).

One more example to understand this better would be a 3000W 240V element. It would only give you about 500W out of your 750W (97.5V) of panels, at 1000W (130V) of panels it will give you almost 900W which might be acceptable to some people since panels only cost $1/W and they happen to have the roof space.

Also, the elements don't care about AC or DC, they are a simple resistor. 50Hz, 60Hz or 200Hz doesn't matter to them. See the Solar Hybrid Specs for power limits.

Most people want the most they can get out of their solar panel purchase so it depends on your situation if you can live with a slight loss or change out your element.

Check the rating sticker on your tank, it will say what the element wattage is.

Q: Why can't I hook up my solar panels directly to the hot water heater?

A: If you are using more than 150 watts of solar power the AC thermostat contacts can arc, weld, burn up or melt together. The thermostat will no longer function properly to prevent overheating of the tank, creating a dangerous condition.

The design of the controller's special CPU is programmed for Maximum Power Point Tracking (MPPT) and also makes the DC into a form of high frequency AC and stops any arcing within microseconds, just like the zero crossing of AC does. The rapidly changing waveform inhibits arcing of the thermostat contacts. Unlike any other MPPT controller, this one is specifically for use in solar water heating using the original factory thermostat.

Try disconnecting a set of 48V solar panels at the terminals sometime, it will throw plasma balls! This is why solar MC4 connectors say do not connect or disconnect when the system is energized or under load, big electrical arcs will ruin the connectors and obviously your thermostat contacts. A DC rated thermostat would be rated for battery power, not this arcing stuff.

Also, without MPPT you will get little daily heat for your investment. The MPPT continually adjusts during the day to get the most power from the Solar Panels. MPPT is especially needed in the mornings and afternoons to keep the most power pumping into the heating element at all times.

Solar Panels are not like batteries, they only put out reasonably efficient usable power (Watts) within a particular voltage and amperage curve going upwards from morning as the sun comes up. MPPT detects and matches that curve to get you the most power it can from the Solar Panels without pulling the panels off their Maximum Power Point, which is what would happen when you apply a full load at any point in the morning or afternoon and drag the panels down with a direct connect. You might get some reasonable power around noon if you can match the panels with the load (element).

MPPT is very effective and needed when using a near 12 ohm load which can pull a "24V" solar panel down to well below 10V where it won't produce much of anything in a off angle situation like mornings or cloudy days. We generally use 3 panels in series so 12 ohms can pull that down even further real easy, like below 2V per panel sometimes. And you really want to use the old style and well tested, dependable mechanical thermostat made for this purpose that came with the tank.

You can throw more power at the direct connect problem, throw double the panels at it, but then you risk overheating the tank when it goes unused (no thermostat, tank hot at sun up), also waste panel mounts, money and space, plus you will still have the problem of getting any reasonable heat on light cloudy days. Why not let a CPU and this fantastic new technology do it the right way?

Q: This can't be MPPT! It's not higher voltage in and lower voltage out!

A: The "MPP" part means Maximum Power Point, the "T" part, "Tracking" means keeping the panel's output (voltage and amps) at it's maximum output WATTAGE at all times. This is independent of the output voltage, which in this particular application of MPPT we want as high as possible. It's easy to confuse this with a common MPPT Charge Controller for batteries, but that is a completely different application of MPPT. A normal MPPT Charge Controller will not work in this application since it's designed for battery operation and DC output, not AC or really, pulsed DC depending on how you want to look at it.

Q: Can I mount the Solar Hybrid Hot Water Controller outside?

A: No. The circuit should be mounted inside away from rain and moisture including morning dew and for solar panel sets with a open voltage above 90V a grounded close-able metal enclosure should be used, such as the hardware store metal electrical disconnect box above.

Q: What is the recommended box and why doesn't it come with one?

A: Depending on the number of panels you want to run, you pick the box and buy it locally, then mount and wire the unit. The hardware store metal electrical disconnect box we recommend for a 2 panel minimum system is the Home Depot or Lowes Model Eaton #DPU222RP $8 and used to mount the device and provide covered protection. [
Click HERE for a link to the Eaton Electrical Box at Home Depot ] We can't sell and ship you a box for $8 and you will probably take a trip there to buy a nice piece of plywood for backing and some wire anyway.

For $8 you get a disconnect switch, wire connection terminals and a nice enclosure with no extra shipping charges!

Do not buy the GE box that looks the same, it's too small inside and the controller won't fit.

For 750W and above you want to use the bigger box, you get it at a electrical supply house. You also buy the $8 one so you can use that nice disconnect switch that comes inside, it has nice connection terminals too.

Q: What are the recommended settings for the upper and lower thermostats on the water heater?

A: It's up to you depending on your lifestyle and needs. If the top heating element is on grid power, we recommend you set that at a lower setting, like around 98F and the lower heating element that's on solar to a higher setting, usually around 135F (scalding concerns should be considered). This way expensive grid power is only used if the tank is really cold. Grid power generally won't be used for small short uses like washing hands or dishes. Since heat rises, you have a little "reserve" of heat in the lower tank that moves up, also consider that the cold water enters from the bottom. If you go completely solar then the settings can be the same as normal or maybe a bit higher. In a normal heater configuration the thermostats will automatically switch to the lower element when the top part of the tank is heated fully. You can also install a timer so the top element doesn't come on in the daytime.

Q: Can I use this on a electric pre-heat tank for my gas water heater?

Yes! A pre-heat tank allows you to increase the amount of hot water available but lower your energy usage with solar power because the water going into your existing tank is heated before it goes in. The existing tank doesn't need to come on as much that way. You should consider that you would have twice the daily heat loss though. Blankets!

Q: What temperature do most people set their tanks to?

Typically, 120°F (49°C) to 125°F (52C) for domestic uses.

When the water temperature exceeds 212°F (100°C), the water will remain a liquid inside the tank, but when the pressure is released as the water comes out the tap the water will boil, potentially inflicting steam burns. Water above about 190°F (88°C) will cause burns on contact. A safety device called a temperature and pressure relief (T&P or TPR) valve, is normally fitted on the top of the water heater to dump water if the temperature or pressure becomes too high. In addition, an expansion tank or exterior pressure relief valve should be installed to prevent pressure buildup in the plumbing from rupturing pipes, valves, or the water heater.

Scalding is a serious concern with any water heater. Human skin burns quickly at high temperature in about 5 seconds at 140°F (60°C), but much slower at 127°F (53°C) it takes a full minute for a first degree burn. Older people and children often receive serious scalds due to disabilities or slow reaction times so you should consider this when adjusting temperatures.

Q: Can I turn the lower element up all the way to save up more solar power?

A: That's what we recommend - to a point, but scalding water isn't fun so you need to consider that whenever you turn up the temp beyond 125F (52C). It can catch you off guard since most faucets run cold till the hot water gets there. Something to consider power wise, the higher the temp goes the harder it has to work against the losses. So pushing it higher takes more energy anyway and if you have that much extra solar power available your tank is probably going to be as good as it is normally.

Q: I want to run a much higher temp but I am worried about scalding, any solution?

A: Yes, several companies sell a Automatic Mixing Valve or Anti Scald Valve that mixes cold water with the hot water. They have a temperature sensing mechanism that automatically adjusts the amount of cold mixed with outgoing hot water to maintain the desired output water temperature. They make them for the whole house or models for sinks and showers.

Q: Will adding a water heater timer help?

A: Yes! Using a simple electrical timer available at Home Depot or Lowes would help keep the upper element off and let the solar panels do their thing in the daytime, saving even more on your power bill. Also helps if you have high Time Of Use TOU tiered power pricing.

Q: Why don't I have to change the element to a DC 24V or 48V version? It says 240V !

A: Because energy/power (watts) is power no matter what and the heating element is just a big resistor. If you put 200W into the element, the water will receive 200W of energy (with a very small loss). The unique thing with this controller is it's ability to adjust to the changing light conditions and different loads on the solar panels using it's special proprietary MPPT programing where it keeps the resistive load always producing as much power as the solar panels can provide at their Max Power Point voltage and amperage. Resistors don't care about AC or DC or 60Hz or 50Hz.

Q: Can I throw 5,000W of panels at it?

A: The idea is to supplement or assist the water heater power usage, not replace it. If your thermostat is off most of the time you will be throwing away perfectly good solar power. We recommend two 24V 220W solar panels for a typical minimum install configured as a hybrid setup as the most cost effective solution for many reasons, one is the lower voltage, another is the cost of installation and with more power you need a bigger box. As you add panels you connect them in SERIES and the voltage goes up but the amperage stays the same so it's easy to expand later. (Around 220W each, panels vary, prices change, a few watts above or below is OK)

The other choice customers have reported as very good is 750W (with bigger box). 750W X 9 hours sun = 6,750 Wh or about 6.7 KWh a day off your bill, not bad, that's over 200 KWh a month! Time your use and conserve and you are in pretty good shape for what you spent on this low cost system. (your daily solar output may vary of course) If you want to go 100% off grid, contact us, but 750W is getting close if people can conserve and time their use, most fluid based systems are around that much energy to the tank and they still have a back up grid element. See the Solar Hybrid Specs

Electronic devices like to run cool. When you push the specs and run higher power you are pushing the electronics to higher temperatures and risking failure when it isn't necessary. This is not a race car you can "soup up", please don't push it.

Q: When I add more panels, is it in parallel or series?

A: Another reason we recommend two 24V solar panels is because as you add more panels, you need to add them in SERIES, always increasing the voltage, the amperage stays the same. DC voltages over about 90V start to become dangerous, so we always recommend that you use a professional electrician to install this device.

You will also need to increase the heat sink size for proper dissipation of heat, the switching mosfet needs to be kept cool, overheating a mosfet is what causes most failures.

You do not want to exceed the maximum voltage for this device, or push it to the limit. You just don't do that with electronic equipment no matter how well it's designed. Be reasonable and conservative. Remember, it's the SOLAR PANEL OPEN CIRCUIT VOLTAGE (Voc) that matters here. Solar panels can produce more voltage than the spec under certain conditions like cold days with scattered clouds (the cloud edge effect is well known). See the Solar Hybrid Specs

We recommend that you start small, monitor things, conserve and time your hot water use, always add a water heater blanket, then see how it goes before adding more panels.

Q: Can I parallel the panels with a normal battery charge controller?

A: If the thermostat clicks off then another controller could take over. When both are active the MPPT would fight with the other controller for power most likely back and forth, which would probably work and depending on the type of charge controller it might work out. If the batteries were charging it would take away from the water heating, most likely in the morning, so you would have to consider that. It's DIY so experiment and see how it works out!

Q: Could I use this with a Wind Turbine?

A: The Solar Hybrid Hot Water Controller is designed for use with solar panels only. Wind Turbines generally have a controller and a battery because they give you erratic power and voltage levels and are not dependable at giving you consistent daily power. However, it may be possible to provide the Solar Hybrid Hot Water Controller with battery power somehow (properly fused of course), and it will provide heat to the hot water tank, but that would be experimental and up to you on how to properly configure it with your Wind Turbine and it's controller and how you would keep it below the rated amps. Check out our PWM Dump Load Controller or GTI Controller product for wind and batteries or contact us for a possible custom solution.

Q: What are the problems with fluid based systems?

A: There was a government study done a few years back that concluded that when solar panel prices get below $1.50 a watt it will be worth going with PV panels instead of a fluid system. They also pointed out some of the problems with a fluid system.

"There are currently over 90 million water heaters in use within the United States (Zogg and Barbour 1996). The number of installed solar water heaters, by comparison, is less than 1 million due to durability and installation issues, as well as relatively high initial costs. Durability issues have included freeze and fluid leakage problems, failure of pumps and their associated controllers, the loss of heat transfer fluids under stagnation conditions, regular replacement of antifreeze and heat exchanger fouling. The installation of solar water heating systems has often proved difficult, requiring roof penetrations for the piping that transports fluid to and from the solar collectors. The solar photovoltaic hot water system described in this paper avoids the durability and installation problems associated with current solar thermal water heating systems (Fanney and Dougherty 1997; Dougherty and Fanney 2001; Fanney et al. 1997)." [
Government Study on PV Solar Hot Water Heating (PDF file) ]

Also overheating problems causing loss of fluids by overflow and ACID problems when grid power is lost and pumps don't work, or when homeowners go on vacation.

When propylene glycol overheats, it turns brown, thickens and stagnates. During stagnation, the glycol starts to break down and becomes more acidic which can eat pipes. A lot of homeowners have found pinhole leaks in their solar collectors, this could be caused by acid eating at the pipes with bigger leaks on the way.

Another thing no one mentions is that fluid based systems also have a grid backup element! They don't talk about how often that comes on. Most systems are pushing about 750W of actual energy to the tank anyway (after losses etc..). That's a lot of expense, hardware, piping, pumps, valves and possible problems compared with a few PV panels and 2 wires.

Pumping water takes power too!

Q: What are the problems with battery / inverter based systems?

A: Batteries are expensive, messy and need maintenance. They have about a 5 year lifespan, some are better, some are worse, then you have to replace them. You have to size your batteries and panels with your daily AC loads which is hard to do since no one uses AC appliances exactly the same way every day. Weather conditions change and so does your power production. It's not a lot of fun always adjusting your loads to your daily system output.

At night your batteries may run down and your inverter shuts off, so you need to somehow automatically switch back to the grid, that's another expensive piece of equipment you need, a transfer relay. Then, every day you have to reset your inverter.

You may want to connect into your electrical box for selected circuits, more expense. Or maybe run extension cords all over the house, nice. Good extension cords are not cheap.

Q: Why do you say it's a partly assembled and tested kit?

A: Depending on the number of panels you want to run, you pick the box and buy it locally, then mount and wire the unit. The Solar Hybrid Hot Water Controller comes as a partly assembled and tested kit, the electronic circuit is fully assembled and tested and mounted on it's heat sink, you provide the enclosure/box, wire and mounting methods. No soldering required. Typically a hardware store metal electrical disconnect box (Home Depot or Lowes Model #DPU222RP $8) is used to mount the device and provide covered protection. [
Click HERE for a link to the Eaton Electrical Box at Home Depot ] We can't sell and ship you a box for $8 and you probably want to buy a nice piece of plywood for backing and some wire from Home Depot anyway.

For $8 you get a disconnect switch, wire connection terminals and a nice enclosure with no extra shipping charges!

Do not buy the GE box that looks the same, it's too small inside and the controller won't fit.

For 750W and above you want to use the bigger box, you get it at a electrical supply house. You also buy the $8 box so you can take out and use that nice disconnect switch that comes inside, it has nice connection terminals too.

Q: Why does it need a bigger box / heat sink for over 500W?

The heat sink is there to dissipate the heat when the device is heating water. It's 97% pass through efficiency, so worse case, 3% of 750W is 22.5W and that needs to go somewhere (max loss basically, it's not always that much). The outside of the properly sized metal box generally gets maybe 10F or 20F above room temperature while heating water, not a big deal. See Other elements tests page

Q: Should I use metal conduit for all the wiring?

A: We recommend using metal conduit for several reasons, first is to protect your expensive wire from the sun, next would be to keep the little critters from eating through the insulation since they do climb on roofs, third would be for fire protection in case of a high ohm contact which would heat up, fourth would be possible lightning protection because typical wire insulation is 500V to 1000V and lightning (100 million volts plus) will seek the ground potential of the metal conduit and POSSIBLY save your equipment, lightning is wild so you really can't protect 100% for a direct strike. Panels and conduit should be grounded as direct to ground as possible.

Q: What size wire do you recommend?

A: We recommend using #12 AWG wire minimum with the Solar Hybrid Hot Water Controller and 5 ft max length "BX" wire (has conduit already) to the heating element, shorter is better, larger diameter wire is better of course, possibly up to #6 for the longer run to the solar panels but remember the voltage is 48V+ so wire loss is less than a normal 24V solar panel system. For the short run you can use solid wire, for the longer run you want to use stranded, the more strands the better (and it's more flexible).

Q: Should I have a outside disconnect?

A: We recommend putting a extra disconnect outside for your own convenience when working on your system (do not put the controller outside) and some fire departments suggest them because they don't know the voltage of your system. Some solar systems run at over 600V and are dangerous to fire personnel. Any disconnect should be labeled. Some codes require a lockable disconnect outside.

Q: What ways can I use to get wire to the lower element?

A: We recommend to simply bend the access panel a little to accommodate the small size #12 "Armored (BX) Electrical Cable" (electrical cable encased in metal sheathing) at the bottom part. While the cover is off, using a hammer, cloth and a large bolt as a form to hammer against works well to create a nice outward bend. Or bend a corner slightly up. With this method it's possible to bend the panel back flat as it was.

If you don't want to bend the cover, make a new cover with a piece of tin, tin shears make it super easy to cut out shapes and you can use the original cover for a template. Or you could simply leave the bottom part of the access panel slightly open, your choice.

If you don't mind drilling holes, this guy (pic at right) drilled a hole next to the element access panel and wired to it that way.

Another way would be to drill a hole directly in the access panel instead of drilling the water heater metal jacket and use flexible METAL conduit like shown in the pic to the right.

One other way is from the access port at the top of the tank. The lower wires do come up to the top element where they are switched with the upper thermostat. You could splice in at that point using wire nuts and feed the wires in and down through the insulation from the upper electrical access port. This method puts the solar wires in with the AC grid wiring, you can accidentally "nick" the AC wires while doing it and the upper thermostat area is live with grid AC at 240V so it's not the best choice, but it is possible.

Wire length from the controller to the element should be kept short, less than 5 feet is good. For the longer run to the panels you want to use stranded wire, the more strands the better (and it's more flexible)

Q: How do you strip back the metal sheathing on "Armored (BX) Electrical Cable"?

A: You grab the metal sheathing with a good pair of pliers and twist it around peeling it like a banana, exposing the wires, and then strip the wires like you normally would.

Q: I want to put a switch or RELAY in for grid or solar, can I do that?

A: All modern USA home tanks have 2 elements so you really don't need to do this.

DO NOT USE A RELAY !

If you are going to do something for a single element tank, you need to make sure the grid will NEVER EVER feed into the Solar Controller!

The best way to do that would be to put a plug on the water heater, like an electric dryer has, and 2 sockets, one for solar the other for grid AC. See this YouTube video of a plug being used: https://www.youtube.com/watch?v=R_LStfeC3lI

Or use a custom made DUAL ELEMENT and TWO THERMOSTATS for a single element tank if it's not time to replace the tank anyway.

If you did use a switch, you would use a "break before make" switch. This type of special switch will stop in the middle off position (break) and then you release it and have to pull the lever again to get it to connect to the other side. It will be expensive. Sometimes it's called a manual generator transfer switch but make sure it ABSOLUTELY "breaks" before it "makes", with some sort of mechanical forced delay.

Use Google and search for "GE 100 Amp 240-Volt Non-Fused Emergency Power Transfer Switch" Model # TC10323R If you look at it you can see it has a lot of room inside to "break before make" during the middle "off" position. Ground the boxes.

DO NOT USE A RELAY !

DON'T DO IT !

A simple AC relay will not guarantee that AC won't go back into the controller! If any AC arcing occurs across the contacts while switching, that energy will also go to the controller and it will go POOF! It also needs to switch BOTH element connections, you don't want the Solar Controller connected to ANY grid connections.

People who have no clue what they are doing ask why, if you have to ask why then you don't know what you are doing so DON'T DO IT ! DO NOT TRY ! It's obvious you have never looked at the inside of a relay.

SMARTASS "KNOW IT ALLS" - This is for you: DON'T DO IT! Did you read this? A simple AC relay will not guarantee that AC won't go back into the controller! You have to ABSOLUTELY GUARANTEE that under ALL CONDITIONS that AC will NEVER EVER get to the controller. Not even for a microsecond! This would not be easy to do DIY and would NOT be a hobby weekend project, you would want a lot of testing and use interlocks, like a NASA engineering project. Do you understand what UNDER ALL CONDITIONS means? Have you seen electronics circuits GLITCH? Yea, it happens! Have you seen the ARCING THAT HAPPENS WHEN A RELAY SWITCHES? Electricity is flowing through that PLASMA! Keep the grid isolated from your solar system, it's easier and safer.

YOU DO NOT WANT 240V AC BACK FEEDING YOUR SOLAR PANELS EITHER! Yea, did you think about that? Just use the plug if you have a single element or something, or get a two element tank, yours is probably ready to leak anyway and a properly designed and TESTED interlocking circuit would cost you way more than a new tank.

"But they do it on some inverters and generators" - Yea, they do, but they are typically designed for that, meaning they can take AC backfeed for a second or something. You are not playing with a battery operated toy here, we are talking 240V and big amps. A GENERATOR TRANSFER "SWITCH" OR BOX WITH A DELAY CIRCUIT IS STILL ONE SIMPLE RELAY !!!

DO NOT USE A RELAY ! ( is that enough times? )

Q: What National Electrical Codes (NEC) might apply to a installation?

A: This is a low voltage DC off grid system not connected to the electrical grid "mains". The lower heating element is disconnected from the electrical grid "mains". For homeowner DIY installed equipment in single-family dwellings it may be exempt in your area, check your local government codes.

Generally speaking, and this is not an exhaustive list, NEC Article 409, 312, 314 and 690. Article 409 covers "Industrial Control Panels", which are enclosures for general use and operating at 600 volts or less containing circuit protection devices, relays, electrical circuits and connections. Article 312.5 requires the use of proper fittings at enclosure openings, to protect and secure the cables and wiring for example, which just makes sense. Article 314.4 requires all metal boxes to be grounded (bonded), which is always a good idea. So generally, Articles 240, 250, 312, 314, 404, 409, 690.

There are other requirements when using systems over 150V and some at over 80V DC stated in Article 690 such as a need for a outside disconnect, DC-GFP (GFI like device) and a DC Series Arc Fault Detector (when they become readily available and reliable).

When enclosed in a metal UL approved box such as the Eaton box, NEC 409 applies as this is electronic control equipment or a "Industrial Control Panel".

When all wires are inside metal conduit and the metal box cover is closed this system is as safe as is humanly possible for electrical equipment of this voltage and amperage which is typically only 8A.

Therefore, the controller is UL 1741 compliant when all wires are inside metal conduit and the metal box cover is closed.

Common sense applies too, it's in a NEMA and UL rated metal box and metal conduit is used.

We always recommend to have a qualified electrician do any installation, especially with voltages over 90V.

Q: What other safety devices could I add to this?

A: Recommended additional safety devices you should add are a Lightning Protector, and at higher operating volts over 80V, a DC Ground Fault detector and a DC Arc Fault detector (when they become readily available and reliable).

Q: Can I use this with batteries?

A: The Solar Hybrid Hot Water Controller is designed for use with solar panels only. The Solar Hybrid Hot Water Controller might be possible to use with battery power somehow (properly fused of course when using batteries), and it will provide heat to the hot water tank, but that would be experimental and up to you on how to properly configure it with your system and it's controller and how you would keep it below the rated amps. Check out our GTI Controller or PWM Dump Load Controller product for wind or battery applications or contact us for a possible custom solution.

Q: I have a really old water heater, should I change out the elements?

A: You may want to. One customer changed his mineral coated elements with new ones and reported a profound difference in performance. If it's really old you may also want to change out the anode at the same time.

Q: What do the things on the back of the solar panel mean?

A: Solar panel sticker on back side specs, general terms (varies per manufacturer):

A: 3 hours is the approximate daily run time for a typical domestic water heater. That's about 405 KWh per month (4500W elements), which is about $56.70 per month or $680 per year at 14c per KWh.

3 hours at 4500W is a lot of power! If you can time your use to accommodate the solar power and do some conservation you are going to go way below that. Remember that the hot water heater doesn't go completely cold overnight, it just drops down a little and needs a boost in the morning. (depending on use of course)

Q: What's more efficient, gas or electric water heating?

A: You can make your own electricity, but not gas, so with solar it's always more efficient to use a electric heater of course. But here's more detailed info...

Water enters residences in the US at about 10 °C (50 °F) (varies with latitude and season). Hot water temperatures of 40–49 °C (104–120 °F) are preferred for dish-washing, laundry and showering; requiring the water temperature to be raised about 30 °C (54 °F) or more, if the hot water is later mixed with cold water. The Uniform Plumbing Code reference shower flow rate is 2.5 US gallons (9.5 L) per minute; sink and dishwasher usages range from 1–3 US gallons (3.8–11 L) per minute.

Natural gas in the U.S. is measured in CCF (100 cubic feet), which is converted to a standardized heat content unit called the therm, equal to 100,000 British thermal units (BTU). A BTU is the energy required to raise one pound of water by one degree Fahrenheit. A U.S. gallon of water weighs 8.3 pounds (3.8 kg). So, to raise a 40-gallon tank of 55 °F (13 °C) water up to 105 °F (41 °C) would require (40 × 8.3 × (105 − 55) / 100,000) BTU, or approximately 0.17 CCF, at 100% efficiency. A 40,000 BTU/h heater would take 25 minutes to do this, at 100% efficiency. At $1 per therm, the cost of the gas would be about 17 cents.

In comparison, a typical electric water heater has a 4500 watt heating element, which if 100% efficient results in a heating time of about 1.1 hours. Since 16,600 BTU is roughly 4.9 kWh, at 13 cents/kWh the electricity would cost $0.64. Operating a shower at 2.5 gpm and 104 °F (40 °C) is equivalent to operating a 19.8 kW appliance [ ref. w computes 13.2 kW, but that is for 20 degree C increase instead of 30 ].[3] In the UK, domestic electric immersion heaters are usually rated at 3 kilowatts.

Energy efficiencies of water heaters in residential use can vary greatly, particularly based on manufacturer and model. However, electric heaters tend to be slightly more efficient (if one omits the power station losses) with recovery efficiency (how efficiently energy is transferred to the water) reaching about 98%. Gas fired heaters have maximum recovery efficiencies of only about 86% (the remaining heat is lost with the flue gases).

( Reference above from http://en.wikipedia.org/wiki/Water_heating )

Q: Where does the energy go when the thermostat opens?

A: Yes, people actually ask this question. It seems to come from the mention of the bigger heat sink.

The heat sink is there to dissipate the heat when the device is heating water. It's 97% pass through efficiency, so worse case, 3% of 750W is 22.5W and that needs to go somewhere (max loss basically, it's not always that much). The outside of the properly sized metal box generally gets maybe 10F or 20F above room temperature while heating water, not a big deal.

If you take a solar panel out in the sun with it's wires just hanging there, where does that energy go? Solar panels do not need to be connected to a load, they can be operated completely open (Voc) or can be completely shorted (Isc).

So the answer is, when the thermostat opens, the element is disconnected, the circuit is not loaded down by the element anymore, the little LED blinks and the circuit waits for the thermostat to close again. Less than a watt is used at that point, metal box goes to room temperature.

The simple answer is, the energy goes nowhere, like a wall switch turns a light bulb off (open circuit).

Q: Can I heat my Spa / Hot Tub / Pool / House / Floor Heat with this?

A: Spa maybe, pool - that's a lot of water.

This is not magic, it's science. Watts are Watts, Energy is Energy. Do you know how many watts your Spa or pool normally takes to heat and for how long? Calculate that to get your answer. Go look at the manufacturers label on the heating unit. Calculate for a few days. Use Google to do energy conversions if needed.

It's possible on a small Spa to heat it up to a point like 90F (32C) where it will use less grid power to bring it up to a usable temp before you get in it. Maybe with lots of solar panels and several elements and controllers you could push it up to the usable temp but that is a lot of water and most of the time it's not in use.

Most Spas START at 300 gallons (1136L) for a small one and are not well insulated, night losses are bad and they generally touch the ground (pools too) so that sucks a lot of the heat away. As the temp goes up, the harder it is to heat because it's working against the heat loss. You will have to figure out a way to detect if the pump is flowing water or risk burning out elements fast. That is usually done with a pressure switch. See the DIY Hot Tub Heating Project page: [ http://techluck.com/solar-hot-water-mppt-spa-hot-tub-heating.php ]

Keep in mind that when you heat water for showers and washing you are talking about maybe 50 gallons sitting in a well insulated INDOOR tank. But it's also a higher temp at the tank.

Space heating is not easy. Again, watts are watts. In a small 10 X 10 ft. room a 1500W Space Heater would be OK in the winter. Heating your whole house is another story. Calculate your normal heating watts before doing anything. See this DIY project and test where it actually worked in a small room but wasn't very practical: [
http://techluck.com/direct-solar-space-heating-system.php ]

Heating a pool is going to take a lot of energy. As said above, find out how much energy is used to heat it now and you can estimate how many solar panels you may need. Consider that it's already outside in the sun, maybe a dark plastic floating cover or painting the pool darker will help.

Q: Weeee! I am going to go completely off grid! Weeee!

A: Do you remember having dark cloudy rainy days?

Going completely off grid is not easy. In this case 750W is pretty close for most people with a little conservation and even gives you some power on light cloudy days!

You still want the grid for those special occasions when your demand goes up or it's a bad solar day. And since most of the time you are using solar, a few KWh here and there won't add up to much at the end of the month. You have to find a balance between what you invest in panels and the cost of a few KWh of grid power.

As for the rest of the home power you need, go watch some YouTube videos of people that have gone completely off grid, large banks of batteries or generators are needed for those bad solar days if you want to not have to change your lifestyle and conserve on those days. Maybe some better technology will come around to replace batteries.

The Solar Hybrid Hot Water Controller is Patent Pending.

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